The present invention relates to a wear indicating friction disc, and more particularly, to a wear indicator for a multiple friction disc aircraft clutch.
Wear indicators, including audible signaling elements, are known for indicating/signaling brake/clutch disc wear. See for instance, Beemer (U.S. Pat. No. 4,049,084), which discloses the use of a secondary frictional material between a primary frictional material and a backing plate for a clutch or brake system. Upon sufficient wear of the primary material, the reaction member comes into contact with the secondary material and produces an audible sound indicating that replacement of the friction member is due. FIGS. 9, 10 and 11 show specific embodiments where the secondary friction material 94/52 is carried in apertures in the primary material.
Mann (U.S. Pat. No. 4,604,604) discloses the use of a vapor emitting wear indicator for use with a brake lining or clutch pad. FIG. 3 shows an embodiment where a capsule 18 including a vapor emitting material is positioned in a sleeve 24 of the lining 14 and will emit a distinct scent and/or colored smoke upon being the lining/pad wearing to the point that the capsule comes into contact with the reactive member.
Campbell (U.S. Pat. No. 5,238,093), Heidenreich (U.S. Pat. No. 5,295,909 and U.S. Pat. No. 5,020,650), Grosspietsch (U.S. Pat. No. 5,908,097), DeVlieg (U.S. Pat. No. 6,659,233), Flotow (U.S. Pat. No. 5,181,593), Müller (U.S. Pat. No. 6,206,158), Gochenour (U.S. Pat. No. 6,296,099), Despres (U.S. Pat. No. 6,357,570), and Ziegler (USPA 2003/0062237) all disclose brake/clutch wear indicators that provide a visual indication of wear of the brake/clutch lining.
Drexl (U.S. Pat. No. 6,040,768) discloses a system for monitoring clutch wear status that uses speed and position information. Hayashi (U.S. Pat. No. 6,276,197) discloses a system that uses an electromechanical sensor 19 for measuring clutch wear. Wang (U.S. Pat. No. 5,712,805) discloses a noise diagnostic system for a vehicle.
Certain Mercedes automobiles use electrical brake wear indicators that insert into the side of the disc brake pads. When the brake pads wear to the point of uncovering the indicator, an electrical path is made through the indicator to signal that the pad needs replacement.
Carbon/carbon composite friction discs are used in a variety of aircraft for brake disc material. As the discs are used, they wear away. Each disc has a designated amount of wear material that can be used. However, an aircraft clutch using the same material often experiences unequal wear between the plates (discs). Therefore, while one plate may still be within acceptable wear limits, another plate may be beyond acceptable wear limits and should be replaced to prevent failure of the clutch plate and clutch and/or to maintain the torque handling capability of the clutch within acceptable limits.
In such an aircraft clutch, there is a need to determine whether one or more clutch plates of the clutch have reached their acceptable wear limits and to signal that this has occurred. Detection of the unequal wear assures proper condition based maintenance while the clutch is still functioning normally.